Impact of Residual Vein Venous Thrombosis in Consecutive Patients with Cancer-Associated Thrombosis Treated with Tinzaparin—A Cohort Study

<b>Background</b>: The role of residual venous thrombosis (RVT) as a risk factor for recurrent venous thromboembolism (VTE) in patients with cancer-associated thrombosis (CAT) remains controversial. <b>Methods</b>: We conducted a cohort study on consecutive patients with CAT treated with tinzaparin recruited between 2007 and 2022. Primary outcome: RVT. Secondary outcomes: identification of variables associated with RVT and the role of RVT in VTE recurrences or clinically relevant bleeding (CRB). <b>Results</b>: Among 511 patients with CAT (age 64.1 years ± 13.4 years; 53.5% males) followed for 17.6 months (p25-75: 7.9-34), 35.8% (n = 183) presented RVT (at 6 months, 55.5%). Variables identified as being associated with RVT were ECOG performance status > 1, metastasis, and cancer location. Within 5 years, there were 57 CRB (11.2%; 95% CI: 8.6-14.2) and 67 VTE recurrences (13.1%, 95%CI: 10.3-16.4). Competing risk analysis identified that RVT at 6 months was associated with VTE recurrence within 5 years (sub-hazard ratio: 2.1; 95% CI: 1.2-3.7; <i>p</i> = 0.006), but not with CRB. Multivariate analysis confirmed that RVT at 6 months (HR: 2.1; 95% CI: 1.2-3.7) and metastases (HR: 1.7; 95% CI: 1.1-2.9) were associated with VTE recurrence within 5 years. <b>Conclusions</b>: RVT is high in patients with CAT. The presence of RVT at 6 months was associated with an increased risk of recurrent VTE over 5 years.